This invention relates to a thin film magnetic head in which at least a part of a magnetic core is composed of a magnetic thin film.
With the recent progress of high density magnetic recording, it has been required to record a signal on a magnetic recording medium having a high coercive force and therefore a magnetic core material having a large saturation magnetic flux density has been needed. Further in order to obtain a high speed treatment of the signal, there has been required a magnetic head exhibiting a high permeability and a high efficiency in a high frequency range. As one of such heads, a thin film magnetic head having a construction as shown in FIGS. 1 and 2 has heretofore to been used.
Referring to these Figures, a numeral 1 denotes a ferromagnetic substrate and a conductor layer 2 is deposited on the substrate 1. The conductor layer 2 is formed by photolithographic technique so as to constitute a winding of the head and covered with an insulator layer 3. An upper magnetic layer 4 made of a material such as Permalloy is deposited on the insulator layer 3 and has a construction such as that it crosses over the conductor layer 2, so as to constitute a part of a magnetic core of the head. A protector layer 5 made of a material such as SiO.sub.2 is disposed so as to cover the above-mentioned components and onto the protector layer 5 is bonded a protector plate 7 of a glass by a bonding layer 6 of a resin. The protector plate 7 is for preventing wear due to a sliding contact between the head and the recording medium.
In the thin film magnetic head as described above, the magnetic layer 4 is made so as to have a direction of easy magnetization perpendicular to the direction of a magnetic flux imparted from the recording medium, in order to have superior characteristics in the high frequency range.
Such anisotropy is apt to be described by a heat cycle. After heating in a heat cycle up to 300.degree. C., the permeability in the direction of easy magnetization becomes about 0.7 times as large as that before the heat cycle. After heating in a heat cycle up to 500.degree. C., the magnetic layer becomes almost isotropic. Because of such characteristics, the bonding of the protector plate 7 must be carried out at a temperature below 450.degree. C. Therefore as the bonding layer 6 a resin which acts as an adhesive at a temperature below 450.degree. C. has been used.
However, since the resin is soft and has a bonding strength, the bonding layer 6 is easily worn, which causes a chipping 9 of the protector plate 7 and eventually, causes a chipping 8 near the gap portion. This has been a serious defect which shortens the lifetime of the thin film magnetic head.